Generally, a rock drill rig (FIG. 1) comprises a movable carrier, a boom and a feed beam connected to the boom via e.g. a feed beam holder. A drilling machine is movable along the feed beam, affecting the drill string to be forced into the ground. The drill string comprises the drill point (drill bit) and the joined rods.
When drilling relatively deep holes, it is important that the drill hole does not deviate from the intended direction, since a deviation may have a negative effect on the final result depending on what the hole is to be used for. One or several drill rod supports are used to guide the drill string, thereby preventing the drill string from deviating.
A drill rod support should not be confused with a clamping device. Drill rod supports are used for guiding the drill string during drilling, on conditions of low friction between drill string and rod support. Whereas clamping devices, such as DE 19909860 and JP 2003 074286, are used for loosening or tightening of the rods when they are removed from the drilled hole, and hence designed to clamp tight around the rods (high friction).
Generally, a drill rod support comprises a pair of support halves. The halves can be moved to and from each other to be opened and closed respectively around the drill string. When the support halves are in their closed position, they are in contact with the drill string via the surface of the recesses, thus guiding (centring) the drill string, but not clamping the drill string.
The recesses of known drill rod support halves form an opening adapted to fit the drill string, by shape and dimension. A common form of recess of the support halves is essentially semi-circular creating a principally circular opening, adapted to fit drill strings with a circular cross section (shown in FIG. 2A).
There are also drill rod support halves which are especially adapted for drill strings with polygonal cross sections (e.g. JP 2003 053724). These halves can thus only be used for a specific rod form and dimension.
A major drawback of known drill rod support halves in that they are adjusted to fit a specific drill string of a specific dimension and shape. One problem with support halves being adapted to fit a certain drill string is, that the drill rod support is subjected to heavy vibration, the drill string and stone dust etc. causing wear of the drill rod support and especially of the drill rod support halves. The fit is satisfactory when the halves are new, but as the support halves are worn, especially by the rotating drill string, the fit between the support halves and the drill string is impaired (shown in FIG. 2B), resulting in poorer guiding. The guiding is worsened the more the halves are worn. The support halves must then be exchanged to maintain adequate guiding of the drill string. Frequent exchanges are time-consuming and increase the costs for equipment.
Another problem in using drill rod support halves adapted to fit a certain drill string is that it results in time consuming exchange of support halves for different strings.